The quality and safety of water suppiles in the U.S. is a topic of major concern. Similarly many commerical and industrial operations use biociles and other toxic substances whose in situ activity is of critical importance in terms of economics, employee health, and environmental responsibility. The primary objectives of this proposed investigation are to further develop the rapid and simple Bioluminescent E. coli water quality monitoring assay developed by Biosyne Corporation. The first of these will be accomplished by selecting strains which respond specifically to low concentration of toxicants such as commerical biocides, insecticides, solvents, heavy metals, etc. by rapidly attenuating their light ouput, such strains will be K12 derivatives hosting a cloned light-controlling lux region from a luminescent marine bacterium. The second aspect of this proposal is the optimization of the present assay to maximize sensitivity and response. Thirdly, a portable bana-held luminometer for field studies and a laboratory instrument will be designed and validated. A large market for this assay system is foreseen which includes metal fabricators (cutting fluid), large scale air-conditioning (cooling towers and legionnaire's Disease prevention), chemical producers (toxic waste monitoring), and government agencies (EPA, OSHA, DOD, DOE, NASA, NIH, etc.).